Question

Basically exactly what the title says. I would like to update the text that a button contains every 1 second when the user presses that particular button. I have noted that when the program doesn’t have focus it works alright and the text refreshes correctly but when I am hovering over the program or when I am trying to click on it’s menu Windows inform me that the program is unresponsive and asks me if I want it terminated. When the loop finishes the program returns to its normal state. Also any action I might have done (like moving it around or closing it) while it was Sleep()-ing is executed after the loop. Here is a bit of code:

case ID_BUTTON_START:
// Code executed when pressing Start Button.
char startButtonText[30];  // Storing next loop text
 for (int i=5; i>0; i--)
    {
       sprintf(startButtonText, "Starting in ... %d", i);
       SendMessage(hwndButtonStart, WM_SETTEXT, 0, (LPARAM)(startButtonText));
       Sleep(1000);
     }

Is this normal? If not what’s causing this?

Answer 1

The WndProc does not process messages asynchronously within an application which means all messages are expected to be handled quickly and a return value delivered immediately. You must not Sleep in the UI thread since it will block other UI events from being processed. Any heavy work or synchronous requests/jobs which are likely to take a long time should be performed in worker threads. There are at least three viable options:

1. Create a new (worker thread) for the task.
2. If the task is likely to be done often, use a thread pool instead.
3. Set and subscribe to timer events.